Welcome back. In the last few lessons, we described the parts of the horse, normal health basics and natural behaviors. Keep those lessons in mind as we go through this lesson on digestion and nutrition. By the end of this lesson you will be able to identify the parts of digestive system of the horse. And better understand how the horses digestive system works. Horses by nature are grazers, eating roughage with their heads down and wandering to get their food. Their ideal meal was intended to be a high fiber, low energy feed eaten throughout the day. Continual access to high fiber feed is what their digestive system evolved to handle. When we don't provide high fiber food, or if we feed to infrequently or feed large meals, digestive upsets will follow. A balanced diet is necessary for all horses to be healthy and thrive. This is especially true for young horses, pregnant and lactating mares, older horses and performance horses. The digestive system pertains to the organs involved in prehension or getting the food into the mouth, chewing, swallowing, breaking down the food into absorbable nutrients and the passage and elimination of waste. The horses digestive tract begins with their mouth and ends at the rectum under the tail. The size of the various parts and their functions are very different from a cow or from human. The total length for a horses digestive tract is over a 100 feet. A horse's digestive system functions best when it is delivered a consistent type of feed. That feed is high fiber, the feed has low sugar content, and the meals are provided in divided portions throughout the day. You'll understand why these four keys are so important to the horse's well being as we explain in more detail, the unique digestive truck of a horse. Horse's lips and teeth are meant for acquiring the food and breaking the raw materials into digestible sizes. When a horse is grazing, he uses his front incisor teeth to get the food into the front of the mouth. If he is eating loose fee such as hay or grain, he picks up the food with the lips. The food is passes to the back of the mouth with the strong muscular tongue. Once in the back of the mouth the cheek teeth, or molars and pre-molars, and strong cheek muscles work to chew, or masticate, the food into smaller moist pieces for swallowing. This is done with the help of very active salivary glands, to keep the food moist and to provide a alkaline or basic environment of the food as it enters the stomach. The tongue helps to get the ball of masticated food into the pharynx, which is the swallowing area, the beginning of the esophagus to be swallowed. This is a slow and enjoyable process for the horse. It can take 10 minutes to consume a pound of grain, and 20 minutes to consume a pound of hay. The pharynx is a muscular sac like section that passes food into the esophagus. It is also part of the respiratory system, which provides passage of air between the nasal cavities and the larynx on the way to the lungs. Just like in people, the airway and the esophagus sit very close to each other in the back of the horse's throat. The horse has a soft palate which is a curtain like structure which prevents food and water from reentering the mouth once it has entered the pharynx. The length of the horse's palate prevents it from inhaling air through its mouth. Horses can only inhale air through their nose and they will often exhale through their mouth. Once past the pharynx, the food enters the esophagus which is a muscular tube about five feet long. It runs down the left side of the neck. You may see a bullous of food or water passing through the esophagus in the depression where the jugular vein lies when your horse swallows. Food and water are massaged into the stomach in one directional waves by the esophageal musculature. There is a very tight and toned connection between the esophagus and the horse's stomach. And this connection prevents vomiting. Horses, unlike humans and dogs and other species, cannot vomit. The only way for food and water to go in the opposite direction of the horses pharynx is to exit through the nostrils. This is why sometimes you may see a horse coughing masticated food and it may appear at the nostrils. Red alert. If you see food coming through the horse's nostrils, something is wrong. And it is likely due to esophageal choke. In humans, choke refers to obstruction of the airway. In horses, choke is obstruction of the narrow esophageal tube. When a large dry pocket of food get stuck in the esophagus, either hay or pellets, this creates the appearance of choke. More food cannot go forward into the stomach because the esophagus is blocked and so it backs up out the nasal passages. This is a situation that is signaled by heavy salivation and head tossing in addition to the presence of green food materials at the nostrils. Choke can resolve on its own but often requires veterinary intervention to dislodge the blocked materials. A phone call to the veterinarian is warranted if you observe your horse displaying the signs of esophageal choke. In some cases, the choke will resolve on its own. But your veterinarian will guide you in your decision making. And it might require that the veterinarian come out and pass a nasal gastric tube to relieve the obstruction. The horse has a simple stomach which is relatively small compared to its overall body size. The capacity is about 4 gallons, this is very important to remember. And it is why it is so important to provide frequent small meals and allow the horse ample time to calmly eat hay in grace. Over filling the stomach not only diminishes the digestive efficiency and comfort of the horse. It can also cause breathing distress to the pressure against the diaphragm and lungs. Remember, the horse cannot vomit. So if it consumes a large quantity of feed in a short period of time, it has trouble relieving the stomach pressure that is created. Horses with stomach pain will display significant signs of colic which is painful behavior associated with the GI tract. The smooth muscle within the stomach compresses the food and the stomach secretes enzymes which begin to break the food down, but the stomach is not the primary organ of digestion. The food in the stomach is layered and slowly moves into the small intestine. There is always some food material being processed in the stomach unless a horse has been without food for a day. If the horse overeats and consumes a quantity of food in a short period of time that is greater than the capacity of the stomach, some of that feed will leave the stomach unprocessed and enter the small intestine, creating indigestion in the next segment of the digestive track. The small intestine is about 70 feet long in the horse. It holds about 12 gallons of relatively liquid food and it is about two to three inches in diameter. Digesting continues in the small intestine where proteins and fats are absorbed. The small intestine forms various coils and curves, which can be problematic if the horse has a build up of gas. Horses suffering from small intestine obstruction are often very painful and have some specific signs on colic exam that indicate that the small intestine is involved. The large intestine is divided into four parts, the cecum, large colon, small colon and rectum, it is about 30 feet long, and holds about 20 gallons of liquefied feed. This section is considered the hindgut of the horse and is the site of fermentation which is the final step in digestion. The hindgut is home to billion of bacteria that produce the enzymes which breakdown the plant fiber into absorbable nutrients. These microbes are essential to the horses survival, because the horse needs the microbes to make the enzymes to digest the fiber. The microbial process of breaking down fiber, takes time and accounts for the slow passage of feed through the large intestine. The cecum is about four feet long, with a capacity of about eight gallons. It is similar to the our appendix in that it is a blind ended sac within the abdomen. It is a large fermentation vat of small pieces of fiber. The cecum opens into the large colon which is about 12 feet long with a diameter of 8 to 10 inches, and a capacity of about 20 gallons. It is usually distended with adjustable food material which is now called ingesta. The last section of the digestive tract is the rectum which is just a few feet long and ends at the anus. Get your pitchfork ready. All of the feed that your horse ingested in the last 24 hours plus the 12 or so gallons of water your horse consumed will equate to about 10 to 12 piles of manure, weighing a total of about 50 pounds. Your normal horse is really passing a pile of manure every 3 to 4 hours. Here is a great resource for managing those manure piles.
